1. Field of the Invention
This invention relates to non-cementitious building materials. More particularly, it relates to an improved lightweight, cement-free building material utilizing sodium silicate as a binder and an expanded siliceous inorganic aggregate.
2. Description of the Prior Art
For many years those skilled in the art have provided a variety of compositions that are useful as low-cost, thermal insulating building materials particularly of use in commercial and residential buildings. The most common of such materials are those having binders comprising cement, such as Portland cement, admixed with a lightweight inorganic aggregate as, for example, vermiculite or perlite. While building materials composed of these materials are generally useful, they are disadvantageously porous and absorb water readily from the ambient atmosphere. Under freeze/thaw conditions, the deterioration in physical properties of these materials is dramatic, and their use as building materials is substantially diminished. Attempts to avoid the water susceptibility of such materials have eventually led to lightweight building materials having good thermal insulation and comprising binders that may include various cements, but also include the silicates of potassium or sodium. Unlike the cement-based materials, these compositions show acceptable water resistance and do not absorb the quantities of water found so disadvantageous in the cement-based compositions. However, they are not entirely immune from water absorption and absorb very small quantities of moisture from the atmosphere. While not being particularly affected under freeze/thaw conditions, a significant manifestation of the small amounts of water absorption appears in the form of efflorescence, a sign that is particularly indicative of the dissolution of the silicate binder. In systems of this nature, this dissolution of the silicate glasses is more rapid in the presence of small amounts of water than with large amounts. The reason for this is that the sodium oxide in silicate glass is leached out, giving a solution of sodium hydroxide, the resulting residual glass being of higher SiO.sub.2 --Na.sub.2 O ratio. It is well recognized that the silica will leach out of this material when the pH of the solution becomes high. Therefore, in the presence of a small amount of water, a given amount of sodium oxide leached from the siliceous glass will give a higher pH than would the same amount when leached into a larger quantity of water. Thus, silicate glass binders, which contain water because drying conditions are not sufficient to convert them to the anhydrous form or because of absorption of small amounts of water from the ambient atmosphere, will be adversely affected. Two major disadvantages occur. The sodium hydroxide formed reacts with carbon dioxide present in the atmosphere, forming sodium carbonate, which manifests itself as efflorescence, e.g. a white powder, on the surface of the board. Secondly, if the sodium hydroxide solution surrounding the glass binder is sufficiently concentrated, the remainder of the silicate glass binder will dissolve, completely destroying any binding capability with any building material and resulting in complete failure of such material. The efflorescence problem can be solved by using the potassium silicate glasses instead of the sodium ones, potassium carbonate not efflorescing as does sodium carbonate. However, potassium glasses are economically disadvantageous when compared to the sodium silicates.
Accordingly, it is an object of the present invention to provide a lightweight, non-cementitious building material that shows little deterioration in physical properties when exposed to ambient atmosphere.
It is a further object of the present invention to provide a lightweight, non-cementitious building material that contains sodium silicate and is non-efflorescent.